The surface of pearlitic grey cast iron was treated using a 2 kW Nd:YAG laser
beam with the final aim to improve its surface properties, mainly for automotive
applications. Two kinds of laser surface treatments were experimentally applied.
In the laser surface hardening approach the surface of cast iron was hardened
simply by passing a laser beam at travel speeds 1-50 mm/s keeping the surface
temperature constant in the irradiated area. Detailed structural analysis of the
layer modified by the laser treatment was performed by optical and scanning
electron microscopy, EDS and orientation imaging microscopy with the electron
back scattered diffraction and microhardness profiles were measured.
Conclusions concerning the mechanism and kinetics of pearlite–austenite
transformation during the laser surface hardening were drawn. The size of the
transformed zone was calculated using a three dimensional model for a Gaussian
beam distribution in accordance with direct observations of laser beam energy
densities. In the laser surface cladding experiments a thick Co-based alloy
coating was created on the cast iron surface using so-called side-cladding set-up
when the powder of additional material is locally molten together with a small
amount of substrate and then rapidly solidified creating a coating with the
metallurgical bond to the substrate. A gradual change of a single processing
parameter was used for an appropriate experimental analysis and statistical
correlation study between main processing parameters and geometrical
characteristics of an individual laser track.
Keywords: grey cast iron, laser surface hardening, laser cladding.